The present invention relates to a method for operating an internal combustion engine having at least one combustion chamber, one induction pipe, and one throttle valve.
In modern internal combustion engines having direct fuel injection and/or having an electronic gas pedal, the quantity of gas to be introduced into the combustion chamber is determined, inter alia, according to the quantity of fuel to be injected into the combustion chamber. This is necessary, inter alia, in order to generate a mixture in the combustion chamber in which combustion-generated emissions and fuel consumption are minimized. In this context, the quantity of gas, or the xe2x80x9cgas charge,xe2x80x9d is defined as a function of the actual position of the throttle valve, because the assumption is made that at a defined throttle position only a certain quantity of gas can reach the combustion chamber.
However, the problem in defining the gas charge of the combustion chamber in this manner is that the throttle valves themselves are manufactured within certain tolerances, so that when different throttle valves are set at the same angle, the result can be differing gas charges in corresponding combustion chambers. The gas charge actually present in the combustion chamber can therefore differ from the gas charge defined by the throttle valve position in ways that are not immediately predictable, which makes the creation of an optimal mixture dependent on the accidental presence of a xe2x80x9cstandard throttle valve.xe2x80x9d
The present invention therefore has the objective of refining a method of the type cited above so that the mixture can always be adjusted with great precision.
This objective is achieved as a result of the fact that the minimum gas pressure is measured that is present in the induction pipe assigned to the combustion chamber at the end of the intake stroke, and that from this a value is determined which better approximates the actual gas charge of the combustion chamber.
The method according to the present invention is based on the following consideration: In an internal combustion engine having one intake valve, the piston at the beginning of the intake stroke is located in the upper dead center and then travels to the lower dead center. In this context, the quantity of gas behind the throttle valve continually expands in volume. This has the consequence that the pressure falls. In the lower dead center, the maximum volume and therefore the minimum pressure is achieved. Shortly thereafter, the intake valve closes. At this point in time, roughly the same pressure exists in the combustion chamber as in the induction pipe. By taking account of the characteristic data of the internal combustion engine, the gas charge in the combustion chamber can be calculated from this minimum pressure. Since this gas charge is calculated from the gas pressure that actually exists in the induction pipe, the leakage through the throttle valve and behind the throttle valve due to manufacturing tolerances is taken into account in the gas charge. This value is therefore more precise and can be used to produce mixtures more precisely. The pressure in the induction pipe is preferably measured by a sensor provided in the induction pipe.
In one very advantageous refinement, a gas charge of the combustion chamber is defined from the actual position of the throttle valve, the defined value is compared with the measured value, and then, if the comparison shows that the difference between the measured and the defined gas charge lies outside of a permissible range, the position of the throttle valve is corrected. Therefore, in this refinement, the gas charge measured from the minimum gas pressure and the gas charge defined by the actual position of the throttle valve are combined with each other. In this context, by determining a permissible range, a range of tolerance created, which makes it unnecessary to resort to control interventions too frequently.
In this context, the correction takes place preferably so that the difference between the measured and the defined gas charge is equal to zero. This means that the gas charge is optimized.
The above-mentioned method is particularly well suited for internal combustion engines that have a plurality of combustion chambers and also is particularly well suited for internal combustion engines in which each combustion chamber or a group of combustion chambers (e.g., a cylinder bank) has assigned to it its own induction pipe and its own throttle valve. For this reason, it is proposed in one refinement that the above-mentioned method be carried out independently for a plurality of combustion chambers having their own induction pipe and especially their own throttle valve. In this way, for each individual combustion chamber or for each group of combustion chambers, a value can be calculated which more closely approximates the actual gas charge of this individual combustion chamber, and the position of the throttle valve. assigned to this combustion chamber can be corrected. In this manner, the emissions and fuel consumption characteristics of the individual cylinders of the internal combustion engine are optimized.
Correcting the position of the throttle valve can take place in varying ways. One possibility is to correct an offset, usually taken into account in calculating the gas charge, and a slope. This offset is a value which makes it possible to take into account the air leakage streams through gaps between the throttle valve and the wall of the induction pipe and through other leakage points between the throttle valve and the combustion chamber. The slope takes into account the multiplicative errors in the throttle valve system. In response to a difference between the value for the gas charge defined by the actual position of the throttle valve and a value calculated on the basis of the minimal gas pressure, it can be assumed that the offset and the slope do not optimally reflect the actual reality. This can be partially compensated for by correcting the offset as proposed in accordance with the present invention. The same applies to the slope. In this context, the correction can take place in a multiplicative manner, meaning a change in the slope, or in an additive manner, meaning a change in the xe2x80x9coffset.xe2x80x9d A correction of the offset and/or the slope is recommended especially in response to generally low pressure levels in the induction pipe, i.e., in an operating state in which the throttle valve is closed relatively far, because in an operating state of this type the aforementioned leakage streams play a relatively large role.
Intervening in the control of the throttle valve position has the advantage over regulating the throttle valve position directly on the basis of the pressure-based gas charge that the optimal gas charge can be achieved more rapidly and without transient effects. Calculating the gas charge on the basis of the throttle valve position makes it possible to react immediately to a change in the driver""s requests. On the other hand, the minimum pressure in one cylinder can only be measured anew after an entire rotation of the camshaft.
At an overall high induction pipe pressure, as is also mentioned in one refinement of the present invention, the regulation of the throttle valve position is influenced. In addition, it is also possible to influence the calculation of a setpoint value of the throttle valve. Both measures make it possible to react quickly to differences between the defined and the measured values.
The precision of the above-mentioned method is even more improved in one refinement which, in calculating the gas charge, takes into account the partial pressure of the internal residual gas.
The present invention also relates to a computer program, which is suited to carrying out the above-mentioned method, if it is executed on a computer. In one preferred refinement of this computer program, it is stored in a storage device, in particular in a flash memory.
Finally, the present invention relates to a control and regulating unit for an internal combustion engine, especially of a motor vehicle, having at least one combustion chamber, one induction pipe, and one throttle valve, the unit defining a gas charge of the combustion chamber from the actual position of the throttle valve. To improve the emissions and fuel consumption behavior of the internal combustion engine, the control and regulating unit is connected to a pressure sensor arranged in the induction pipe, and it determines a value that more closely approximates the actual gas charge from the minimal gas pressure existing in the induction pipe assigned to the combustion chamber at the end of the intake stroke.
Especially preferred is the refinement of the control and regulating unit, in which, if the comparison shows that the calculated gas charge of the combustion chamber does not roughly correspond to the defined gas charge, then a correction signal for the position of the throttle valve is generated.
Finally, a control and regulating unit of this type is particularly advantageous if it is suited for internal combustion engines having a plurality of combustion chambers and a plurality of pressure sensors and throttle valves each assigned to one combustion chamber. This is the case in the refinement in which the control unit is connected to a multiplicity of pressure sensors, each assigned to one combustion chamber, and, in particular, generates a plurality of independent correction signals for the corresponding throttle valves.